1. Field of the Invention
The present invention relates to a parallel link robot using a delta type parallel link mechanism for positioning a mounting member equipped with an end effector three-dimensionally.
2. Description of the Related Art
FIG. 11 is a perspective view of a parallel link robot in the prior art. As shown in FIG. 11, the parallel link robot 100 of the prior art mainly includes a base 110, a movable plate 120, and three links 200a to 200c coupling the base 110 and movable plate 120. Note that, the movable plate 120 is provided with a mounting member 190 for a not shown end effector.
As can be seen from FIG. 11, the link 200a is comprised of a drive link 210a extending from the base 110 and two driven links 220a, 230a extending from the movable plate 120. These are coupled with each other by spherical bearings. Further, the base 110 includes an actuator 130a driving the drive link 210a. Note that, the other links 200b, 200c are similarly configured. By separately controlling the actuators 130a to 130c of these links 200a to 200c, it is possible to make the movable plate 120 move by three degrees of freedom (first axis to third axis) and position it at a desired position.
As shown in FIG. 12, in recent years, a parallel link robot 100 further increasing by one the degrees of freedom over the configuration shown in FIG. 11 has been spreading. The parallel link robot 100 such as shown in FIG. 12 is also disclosed in Japanese Examined Patent Publication (Kokoku) No. 4-45310 and International Publication of Translated Version No. 2002-532269. Note that, in FIG. 12 and the later explained FIG. 13, for simplification, the actuators 130a to 130c are omitted.
In FIG. 12, an additional actuator 130d for a fourth axis is arranged on the base 110. Further, an additional link 200d couples the actuator 130d and movable plate 120. As shown in FIG. 12, the link 200d includes a drive shaft 250 coupled by a universal joint. The base 110 and movable plate 120 change in relative positions, so the drive shaft 250 is configured extendably. Therefore, even when the base 110 and the movable plate 120 change in relative positions, the link 200d can track this and therefore the mounting member 190 can be made to turn about the fourth axis in the arrow direction of FIG. 12.
FIG. 13 is a schematic view of a parallel link robot in the prior art increasing by a further one the degrees of freedom over the configuration shown in FIG. 11 and is disclosed in U.S. Pat. No. 4,976,582. In FIG. 13, the additional actuator 130d is directly arranged on the movable plate 120. For this reason, the mounting member 190 coupled with the movable plate 120 can be easily made to turn in the arrow direction about the fourth axis.
However, in the configuration shown in FIG. 12, there are limits to the extendable length of the drive shaft 250. As can be seen from FIG. 12, the drive shaft 250 is comprised of a cylinder and rod. Usually, the shortest length of the drive shaft 250 is the longer of the cylinder and the rod, while the longest length of the drive shaft 250 is the total of the lengths of the cylinder and rod. Therefore, the possible range of operation of the movable plate 120 is limited to one between the longest length and shortest length of the drive shaft 250.
FIG. 14 is a partial enlarged view of a parallel link robot in the prior art. As shown in FIG. 14, the rod of the drive shaft 250 is included in a link 200d through a universal joint 251. However, the universal joint 251 interferes with other parts as the bending angle α shown in FIG. 14 becomes larger (see part enclosed by one-dot chain line in FIG. 14). From this, the possible range of operation of the movable plate 120 is also limited by the bending angle at the universal joint 251.
Furthermore, in the configuration shown in FIG. 13, the actuator 130d is relatively heavy, so the movable plate 120 is remarkably limited in acceleration/deceleration performance. For example, when the end effector of the parallel link robot 100 engages in simple reciprocating motion, the limited acceleration/deceleration performance results in the number of reciprocating operations per unit time decreasing and therefore the processing ability falling.
Further, in the case of use in an environment where the movable plate 120 is exposed to an acid or other corrosive solution, the actuator 130d may be splashed with the corrosive solution. In such a case, the actuator 130d will malfunction and the degrees of freedom of the mounting member 190 will be reduced by one. For this reason, at least the actuator 130d and its wiring have to be suitably protected by a protective cover (not shown) etc.
In the case of the configuration shown in FIG. 12 and FIG. 13, due to the dimensions of the drive shaft 250 or space for arrangement of the actuator 130d, increasing by one the degrees of freedom is the limit. This type of parallel link robot 100 is currently available on the market.
In this regard, FIG. 15A and FIG. 15B are perspective views of parallel link robots increasing by a further two or three the degrees of freedom compared with the parallel link robot shown in FIG. 11. In FIG. 15A, the mounting member 190 of the end effector is rotatably attached through an intermediate member 160 to the movable plate 120. Furthermore, in FIG. 15B, the mounting member 190 is rotatably attached through two intermediate members 160, 170 to the movable plate 120.
However, addition of such intermediate members 160, 170, as shown in FIG. 13, means that, when placing the additional actuator 130d on the movable plate 120, due to their weight, the acceleration/deceleration performance of the movable plate 120 will be further limited. Further, as shown in FIG. 12, when using an extendable drive shaft, an extendable additional drive shaft is required for increasing the degrees of freedom. Due to the physical dimensions of the intermediate members 160, 170, this leads to further limitation of the possible region of operation of the movable plate 120. For this reason, while increasing by a further two or three the degrees of freedom of the parallel link robot shown in FIG. 11 is theoretically possible, practical realization is difficult.
FIG. 16A is a perspective view of another parallel link robot in the prior art, while FIG. 16B is a partial cross-sectional view of the parallel link robot shown in FIG. 16A. In these FIG. 16A and FIG. 16B, the additional actuator 130d is arranged on the movable plate 120. Further, the mounting member 190 has a suction pad 780 attached to it as an end effector.
As shown in FIG. 16A and FIG. 16B, a suction air tube 790 for giving suction force to the suction pad 780 is coupled through a rotation absorption unit 800 to the suction pad 780. The rotation absorption unit 800 can freely rotate and thereby performs the function of preventing the suction air tube 790 from becoming wound around other members when driving the additional actuator 130d etc.
However, the rotation absorption unit 800 is arranged between the suction pad 780 and the mounting member 190, so the distance between the mounting member 190 and the suction pad 780 has to be made longer. For this reason, in the prior art, there was the problem that the suction pad 780 became larger in size and more easily interfered with the workpiece W. Further, when using an end effector which cannot mount a rotation absorption unit 800 or when an electrical cable for the end effector is necessary, when driving the additional actuator 130d etc., there was also the problem that the piping relating to the end effector, for example, the air tubes, or wiring, for example, the electrical cables, would become wound around other members.
The present invention was made in view of this situation and has as its object the provision of a parallel link robot designed to increase the degrees of freedom without narrowing the possible region of operation and without lowering the acceleration/deceleration performance.